The present invention relates to a semiconductor laser and, more particularly, to a laser device construction which ensures stable operation.
A semiconductor laser enjoys a limited period of life depending on deterioration of mirrors which function as the light emitting facet. Furthermore, a semiconductor laser may be damaged by way of the mirrors if the semiconductor laser is driven at a considerably high optical power. The maximum optical power for catastrophic optical damage (referred to as P.sub.max hereinafter) is about 10.sup.6 W/cm.sup.2 in a conventional semiconductor laser.
It is desirable to increase the P.sub.max to achieve stable high power oscillation. Furthermore, the absorption of the high density laser beam near the mirrors must be reduced as low as possible in order to minimize the mirror deterioration.
To achieve the above effects, a window structure laser has been proposed in, for example, Appl. Phys. Lett. 15 May, 1979 P. 637. Another structure has also been proposed wherein a material is doped near the mirrors, the material having a wider band-gap energy than that of the active layer.
Generally, the conventional window structure semiconductor laser does not have the optical waveguide formed in the window region along the junction. Thus, the laser beam diffuses in the window region so as to reduce the beam amount directed to the stimulated region after reflection at the mirror. This will reduce the oscillation efficiency, and will increase the threshold current.
Accordingly, an object of the present invention is to increase the oscillation efficiency in a window structure semiconductor laser.
Another object of the present invention is to provide a semiconductor laser which stably emits the laser beam in the visible spectral range.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, an optical waveguide is formed in the window region, whereby the beam waists for the field confined along and perpendicular to the junction exist at the mirror. More specifically, a V-shaped groove is formed in the substrate. Both a crescent active layer and a plane active layer are formed in the stimulated region and the window region, respectively, through a liquid phase epitaxy method under the same condition. This construction is named the window V-channeled substrate inner stripe (referred to as VSIS hereinafter) laser.
The thus formed window region functions to suppress the higher transverse mode generated in the stimulated region so that only the fundamental transverse mode is transferred in the window region and developed through the mirror. The window VSIS laser of the present invention has low threshold current because the current is perfectly confined in the V channel by the inner stripe.